Experiments aimed at the elucidation of the chemistry and mechanism of Bu-nucleic acid protein photocrosslinking are being performed. Deuterium labeling experiments and quantum yield measurements of the photoreduction of 5-bromouracil indicate free radical and ionic pathways. N-acyl amino acid amides chemically linked to 5-bromouracil at the 6-position are being synthesized and investigated for photochemical reactivity as a model for the photochemistry of a nucleic acid protein complex. The results of this investigation will lead to the development of the Bu-nucleic acid protein photocrosslinking techniques as a powerful method for the study of important protein-nucleic acid interactions.